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Virtue can bring its own reward. If the Government could bring itself to do the right thing with the Electoral Commission's final report on improvements to MMP, it might be surprised.

On paper the recommended changes would make it much harder for National to find partners for a third term. The abolition of the one-seat rule would penalise Act and United Future, and the suggested abolition of "overhang" seats would have left the three of them one seat short of a majority in the present Parliament.

That calculation excites opposition parties as much as it dismays National and its partners, but all of them need to broaden their view. The opposition seems not to have noticed that neither Act nor United Future benefited from the one-seat rule at the last election. Neither gained a high enough party vote to qualify for more seats than the single electorate each won.

Yet their solitary seats were still essential to the Government's survival. Abolishing the possibility for them to gain a few more seats would not necessarily rid the system of the "teagate" stunts that supposedly have discredited the one-seat rule. Abolishing "coat-tail" seats might simply increase the number of nominally independent candidates standing with the endorsement of a major party in its safe electorates.

In fact, that appears to be the reason the commission has recommended abolishing the overhang. Parliament could have too many additional seats if the winners of single electorates no longer had a share of the party vote. Instead, the commission has suggested the size of Parliament be held at 120 seats and parties that win a single electorate would increase the ratio of electorate to list seats.

In response to concern that the number of list seats would drop too low, the commission's final report suggests that the ratio should not be allowed to fall below 60:40. Once population growth lifts the number of electorates to that ratio, Parliament should be enlarged with the population.

Good electoral law requires legislators on both sides to put self interest aside and vote on sound principles. The single electorate qualification for proportional representation is a needless exception to the threshold that is designed to limit the number of parties in Parliament.

Thresholds were designed to reconcile the conflicting electoral virtues of diverse representation and stable government. The 1986 royal commission recommended a threshold of 4 per cent of the nationwide vote. Parliament set it at 5 per cent. Now the Electoral Commission proposes it be reduced to 4 per cent, though it believes even 3 per cent might be high enough for reasonable stability.

National's submission to the Electoral Commission calculated that its proposals would have reduced the ability of both main parties to maintain a stable government after the elections of 1996, 2005, 08 and 2011.

Under MMP's complicated formula for allocating list seats, a 4 per cent threshold would have reduced both major parties' allocation by two seats.

Unmoved by National's mathematics, the commission has reaffirmed its belief that parliamentarians would continue to make stable governing arrangements.

Its confidence is well placed. Even minority governments have proved stable.

National should draw the same confidence that minor parties probably will always respect the country's choice of which of the main parties it prefers to be the government. National can afford to do the right thing.